This invention relates to a process for polymerizing propylene with a fluorenyl-indenoindolyl catalyst precursor in the presence of an activator to obtain high molecular weight polypropylene with little or no isotacticity and low levels of syndiotacticity.
Polymers of propylene are well known and are characterized by their molecular weight and by the stereoregularity of the monomer units. By xe2x80x9cstereoregularity,xe2x80x9d we mean whether the recurring units are present in the isotactic, syndiotactic or atactic configuration. These features affect polymer processability and physical properties. Dependent upon the end use application, different properties are desirable.
Catalyst precursors that incorporate a transition metal and an indenoindolyl ligand are known. U.S. Pat. No. 6,232,260 discloses the use of transition metal catalysts based upon indenoindolyl ligands. There is no indication of stereochemical control. Pending application Ser. No. 09/859,332, filed May 17, 2001, discloses a process for the polymerization of propylene in the presence of a Group 3-5 transition metal catalyst that has two non-bridged indenoindolyl ligands wherein the resulting polypropylene has isotactic and atactic stereoblock sequences. Pending application Ser. No. 10/123,774, filed Apr. 16, 2002, discloses a process for the polymerization of ethylene in the presence of a Group 3-10 transition metal catalyst that has two bridged indenoindolyl ligands.
Propylene polymerizations using fluorenyl-cyclopentadienyl and fluorenyl-indenyl catalysts were reported in Macromol. Rapid Commun. 20, 284-288 (1999) to give polymers with several different tacticities including some within the desired range. However, the tacticity varied widely with polymerization temperature and no indication of polymer molecular weight was given.
Propylene polymerizations using fluorenyl-indenyl catalysts were reported in Organometallics 19 3767-3775 (2000) and references cited therein to make a broad range of tacticities. They report that 2-methyl group and 5,6-substitution on the indenyl ligand are necessary requirements to obtain a high enough molecular weight. With these substituents, the level of mmmm pentads was greater than 25%. Without these substituents, they reported one catalyst precursor that gave a lower amount of mmmm pentads, but the highest reported Mw was 83,000. J. Am. Chem. Soc. 121 4348-4355 (1999) gives results for twelve polymerizations with a 2-methyl-5,6-cyclopentyl substituted complex; the amount of mmmm pentads varied from 20 to 72% dependent upon the polymerization temperatures with the amount generally increasing with increasing polymerization temperature. This system was also studied in WO 99/52950 and WO 99/52955 and polymers with mmmm pentads between 25-60% were disclosed. Macromolecules 35 5742-5743 (2002) studied both the zirconium and hafnium catalysts and reported some advantages using borate activators. However, for any polymerizations done at 20xc2x0 C. or higher, the amount of mmmm pentads varied from 24-54%.
A bis-fluorenyl catalyst system has been reported in Organometallics 15 998-1005 (1996) and U.S. Pat. Nos. 5,596,052 and 5,945,496 to give high molecular weight polypropylene, but the pentads were not reported. A subsequent publication by many of the same authors, Macromol. Chem. Phys. 202 2010-2028 (2001) indicated that the level of mmmm pentads was about 2%. This subsequent paper reported work done with substituted bis-indenyl systems. A bis-isopropylindenyl system with three different bridging groups is disclosed. One gave a very low Mw of 9600 and no tacticity was reported. For the other two polymers, one had 15.6% mmmm pentads and the other 25.5%.
Despite the considerable work done in this area, there are very few processes known to produce high molecular weight, low tacticity polypropylene. All processes behave differently and there is often a tradeoff in useful temperature range, activity, polymer properties or process robustness. Therefore, there is a need for a good process to prepare polypropylene with all three of the desired features. Polypropylene with all three features, namely high molecular weight, low isotacticity and low syndiotacticity should have improved properties such as improved transparency, improved flexibility and improved elastic properties.
The invention is a process to polymerize propylene to give a polymer with high molecular weight and low degrees of isotacticity and syndiotacticity. In particular, the polypropylene has tacticity such that mmmm is 0-20% and rrrr is 0-60%. If a polymer is completely isotactic, it can be too stiff for many applications. The high molecular weight improves strength and mechanical properties. The combination of all three features should give improved mechanical properties, toughness, strength and thermal properties.
The polymerization process is done in the presence of an activator and a fluorenyl-indenoindolyl catalyst precursor.
The tacticity of a polymer affects its properties. The term xe2x80x9ctacticityxe2x80x9d refers to the stereochemical configuration of the polymer. For example, adjacent monomer units can have either like or opposite configuration. If all monomer units have like configuration, the polymer is xe2x80x9cisotactic.xe2x80x9d If adjacent monomer units have opposite configuration and this alternating configuration continues along the entire polymer chain, the polymer is xe2x80x9csyndiotactic.xe2x80x9d If the configuration of monomer units is random, the polymer is xe2x80x9catactic.xe2x80x9d When two contiguous monomer units, a xe2x80x9cdiad,xe2x80x9d have the same configuration, the diad is called isotactic or xe2x80x9cmesoxe2x80x9d (m). When the monomer units have opposite configuration, the diad is called xe2x80x9cracemicxe2x80x9d (r). For three adjacent monomer units, a xe2x80x9ctriad,xe2x80x9d there are three possibilities. If the three adjacent monomer units have the same configuration, the triad is designated mm. An rr triad has the middle monomer unit having an opposite configuration from either neighbor. If two adjacent monomer units have the same configuration and it is different from the third monomer, the triad is designated as having mr tacticity. For five contiguous monomer units, a xe2x80x9cpentad,xe2x80x9d there are ten possibilities. They are mmmm, mmmr, rmmr, mmrr, mrmm, rmrr, mrmr, rrrrr rrrr, and mrrm. A completely syndiotactic polymer would have all rrrr pentads while a completely isotactic polymer would have all mmmm pentads. The configuration can be determined by 13C nuclear magnetic resonance spectroscopy as described in Macromolecules 8 687 (1975) and in Macromolecules 6 925 (1973) and references cited therein. For more information on polymer stereochemistry, see G. Odian, Principles of Polymerization, 2nd edition, pages 568-580 (1981).
The configuration of the monomer units affects the polymer properties. For example, highly isotactic polypropylene readily forms a crystalline structure and has excellent chemical and heat resistance. The polypropylene made by the process of the invention is characterized in that it has low levels of isotacticity and low levels of syndiotacticity. By low levels of isotacticity, we mean the percent of pentads having mmmm configuration is less than 20%, preferably more than 2% and less than 10%. By low levels of syndiotacticity, we mean the percent of pentads having rrrr is less than 60%, preferably more than 10% and less than 25%. Because of the low levels of syndiotacticity and isotacticity, the polymer is predominantly or even completely amorphous and generally has no melting point. It is transparent, flexible and has good elastic properties.
The polymer has high molecular weight. By high molecular weight, we mean the weight average (Mw) molecular weight is greater than 65,000 and preferably greater than 100,000. The Mw can be measured by gel permeation chromatography and affects polymer properties such as elasticity. Generally, the elastic properties such as tensile set and stress recovery improve with increasing molecular weight.
The polymer is prepared by polymerizing propylene in the presence of an activator and a fluorenyl-indenoindolyl catalyst precursor. The preferred catalyst has a fluorenyl ligand bridged to an indenoindolyl ligand. An indenoindolyl ligand derives from an indenoindole compound. By xe2x80x9cindenoindole compound,xe2x80x9d we mean an organic compound that has both indole and indene rings. The five-membered rings from each are fused, i.e., they share two carbon atoms.
The catalyst precursor preferably has the general structure: 
where M is a Group 3-10 transition metal. Preferably, M is a Group 3-5 transition metal and more preferably M is zirconium. L1 is an indenoindolyl ligand and L2 is a fluorenyl ligand. Preferably, L1 and L2 are bridged to each other through a divalent radical. L is a ligand and is preferably selected from the group consisting of halogen, alkoxy, aryloxy, siloxy, dialkylamino, diarylamino, and hydrocarbyl groups. Labile ligands such as halogen are particularly preferred. X is an integer that satisfies the valence of M.
More preferably, the catalyst precursor has the structure: 
in which R1 is selected from the group consisting of C1-C30 hydrocarbyl, C1-C6 halocarbyl, C1-C30 halohydrocarbyl and trialkylsilyl; each R2 is independently selected from the group consisting of R1, H, F, Cl, Br and C1-C6 alkoxy; G is a divalent radical selected from the group consisting of hydrocarbyl and heteroatom containing alkylene radicals, diorgano silyl radicals, diorgano germanium radicals and diorgano tin radicals; M is a Group 3 to 10 transition metal; each L is independently selected from the group consisting of halide, alkoxy, siloxy, alkylamino, and C1-C30 hydrocarbyl and x satisfies the valence of M.
Methods for making indenoindole compounds are well known. Suitable methods and compounds are disclosed, for example, in U.S. Pat. Nos. 6,232,260 and 6,440,889, the teachings of which are incorporated herein by reference, and references cited therein, including the method of is Buu-Hoi and Xuong, J. Chem. Soc. (1952) 2225. Suitable procedures also appear in PCT Int. Appls. WO 99/24446 and WO 01/53360.
The complexes can be made by any suitable method; those skilled in the art will recognize a variety of acceptable synthetic strategies. See especially PCT Int. Appl. WO 01/53360 for suitable routes. Often, the synthesis begins with preparation of the desired indenoindole compound from particular indanone and arylhydrazine precursors. In one convenient approach, the indenoindole is deprotonated and reacted with a substituted fluorenyl compound to attach the fluorenyl compound through a bridging group. Another strategy employs the reaction of a fluorenyl anion with a substituted indenoindole compound. In both syntheses, the resultant fluorenyl group bridged to the indenoindole group can then be reacted with two equivalents of a strong base to form the dianion. Reaction of the dianion with a suitable metal compound affords the catalyst precursor. Any convenient source of the transition metal can be used to make the catalyst precursor. The transition metal source conveniently has labile ligands such as halide or dialkylamino groups that can be easily replaced by the dianion of the bridged fluorenyl-indenoindolyl ligand. Examples are halides (e.g., TiCl4, ZrCl4), alkoxides, amides, and the like.
The catalyst precursor is activated. Suitable activators include alumoxanes, alkyl aluminums, alkyl aluminum halides, anionic compounds of boron or aluminum, trialkylboron and triarylboron compounds. Examples include methyl alumoxane (MAO), polymeric MAO (PMAO), ethyl alumoxane, diisobutyl alumoxane, triethylaluminum, diethyl aluminum chloride, trimethylaluminum, triisobutylaluminum, lithium tetrakis(pentafluorophenyl) borate, lithium tetrakis(pentafluorophenyl)aluminate, dimethylanilinium tetrakis(pentafluorophenyl)borate, trityl tetrakis(pentafluorophenyl)borate, tris(pentafluorophenyl)borane, triphenylborane, tri-n-octylborane, the like, and mixtures thereof.
Selection of activator depends on many factors including the catalyst precursor used and the desired polymer properties. In one preferred embodiment, the catalyst precursor is premixed with a solution of the activator prior to addition to the reactor. Preferably, the catalyst precursor and activator solution are premixed for a period of time between ten minutes and two hours. When the catalyst precursor is premixed with a solution of the activator, it is preferable to use a portion of the activator and to add the remainder of the activator to the reactor prior to the addition of the premix. In this embodiment, preferably an alkyl aluminum compound is added to the reactor prior to the addition of the premix.
Optionally, the catalyst is immobilized on a support. The support is preferably a porous material such as inorganic oxides and chlorides, and organic polymer resins. Preferred inorganic oxides include oxides of Group 2, 3, 4, 5, 13, or 14 elements. Preferred supports include silica, alumina, silica-aluminas, magnesias, titania, zirconia, magnesium chloride, and crosslinked polystyrene.
Many types of polymerization processes can be used. The process can be practiced in the gas phase, bulk, solution, or slurry. The polymerization can be performed over a wide temperature range. Generally, lower temperatures give higher molecular weight and longer catalyst lifetimes. However, since the polymerization is exothermic, lower temperatures are more difficult and costly to achieve. A balance must be struck between these two factors. Preferably, the temperature is within the range of about 0xc2x0 C. to about 150xc2x0 C. A more preferred range is from about 20xc2x0 C. to about 70xc2x0 C.
The catalyst activity can vary based upon the structure of the catalyst precursor, the polymerization temperature and impurities that may be present in the reactor. Generally, the higher the activity the better since poor activity results in more catalyst precursor being needed which increases cost and increases the amount of residual transition metal in the polypropylene. Preferably, the activity will be more than 100 kg polypropylene per gram transition metal per hour. More preferably, the activity will be more than 200 kg and most preferably, more than 400 kg polypropylene per gram transition metal per hour.
The unique structure of these polymers makes them excellent blend components. The high molecular weight and low tacticity should give blends with enhanced properties such as improved flexibility and elastic properties. The polymers can be blended with any of several addition or condensation polymers or copolymers such as polypropylene, polystyrene, polyvinyl alcohol, polyvinyl chloride, EPDM, polyamides or polycarbonate. Preferably, the blend is with polyolefins such polypropylene, polyethylene or LLDPE. Of these, a preferred blend is with polypropylene and a particularly preferred blend is with isotactic polypropylene.